You just sent a request to the SDN controller, and after a little while, the result code came back as a 504 status code. What most likely happened?

A status code of 504 means that the command that was sent to the server did not return in a timely fashion and timed out. A status code of 400 would depict that the command is missing parameters. If a command is restricted for the authentication supplied, a status code of 403 would be returned. If a service is down or improperly responding, a status code of 500 would be returned.